1 . Field of the Invention
The present invention relates to a data polling method and a digital instrumentation and control system for atomic power plant using the method.
2 . Description of the Related Art
A digital control system for atomic power plant needs to be reliable, so it needs to be a system in which, when a failure occurs, its cause can be accurately determined. So, in the system, the reliability of input data input from the outside, such as pres sure of pressurizer, temperature of heater or auxiliary machine open/close status, is determined by appending to the input data its associated reliability data,  such as for determining whether the input data is normal or abnormal.
In order to determine the reliability of input data, data polling is performed between a central processing unit (CPU) equipped in a digital controller system for atomic power plant and an input module as an input unit for input data. Then, reliability data is appended to the input data and the CPU outputs determination data.
However, in a conventional digital controller system for atomic power plant, the data polling period of the equipped CPU is not synchronized with the data update period of the input module, and also, an input module failure detection time for the input module to detect a failure is long relative to the data polling period of the CPU.
Thus, the data polling period of the CPU may be changed to retrieve data from the input module. For example, though in a different technical field, JP-A-2003-259469 (Patent Document 1) discloses a wide area management system for water utility in which a polling period is changed for periodic data collection, self-check or the like.
[Patent Document 1] JP-A-2003-259469 (in paragraph 0032)
However, the Patent Document 1 only discloses that a polling period is changed for periodic data collection, self-check or the like, but does not disclose a specific method for changing the polling period.